Many optical devices, such as some microscopes, telescopes and night vision devices, are viewed with binocular vision but only use a single objective lens arrangement. In such systems, when a single source image is viewed the light from the image must be divided into two separate corresponding optical outputs in order to allow for binocular viewing. Traditionally, the division of a single source image into two corresponding binocular images has been accomplished by utilizing a collimator lens assembly, a beam splitter and two diopter cell assemblies. The collimator lens assembly re-images a source image at a substantially infinite conjugate. As such, the rays of light leaving the collimator lens assembly are substantially parallel. The parallel light is then evenly divided by the beam splitter and directed toward the diopter cell assemblies. The diopter cell assemblies provide optical power to the split beam, thereby either diverging or converging the parallel beam path, and directs the split image into the two eyepiece lens assemblies utilizing a mirror, prism or the like. See U.S. Pat. No. 5,157,553 issued on Oct. 20, 1992 entitled COLLIMATOR FOR BINOCULAR VIEWING SYSTEM by E. N. Phillips, et al. and assigned to ITT Corporation the assignee herein. That patent describes a prior art collimator assembly and related optical elements in a binocular viewing system.
Binocular viewing system that utilize only a single objective lens assembly are common in the design of night vision devices. The use of a single objective lens in a night vision device permits the use of only a single image intensifier tube within the assembly, thereby minimizing the cost and complexity of the system. For instance, in FIG. 1, there is shown a block diagram schematic of a prior art AN/PVBS-7B night vision device 10 commercially manufactured by ITT Corporation, the assignee herein. Referring to FIG. 1, it can be seen that a single objective lens assembly 12 is positioned at one end of the device 10. The objective lens assembly 12 focuses impinging infrared energy onto the image intensifier tube 14, which converts impinging infrared energy into a visible image. The visible image passes through a collimator lens assembly 16 that reimages the visible image at a substantially infinite conjugate. The infinite conjugate image is divided evenly by a beam splitter 20 and is directed toward the left and right diopter cell assemblies 22, 24 respectively. In each of the two diopter cell assemblies 22, 24, the split, infinite conjugate image passes through a lens 26 and is reflected off a mirror 28 toward either the left or right eyepiece lens assembly 30, 32, where the image is viewed with binocular vision. Typically, the left and/or right eyepiece lens assembly 30, 32 are adjustable back and forth in the directions of arrow 33, so as to allow the eyepiece lens assemblies 30, 32 to be adjusted to the specific eye spacing of an individual. For this reason, the diopter cell assemblies 22, 24 are commonly held within slots 36, 38 on a support member 40. As such, the diopter cell assemblies 22, 24 can move back and forth as a unit with the eyepiece lens assemblies 30, 32.
Referring to FIGS. 2 and 3, the construction of a typical prior art diopter cell assembly 24 can be described. As can be seen, light enters the diopter cell assembly 24 from the beam splitter through a lens element 26 that adds an optical power to the infinite conjugate beam. Once the light enters diopter cell assembly 24, the light reflects off a mirror 28 that alters the path of the light by 45 degrees. In the shown prior art diopter cell 24, the mirror 28 is flat and has an elliptical shaped profile. The elliptical shape of the mirror 28 is required in order for the mirror 28 to properly fit within the housing of the diopter cell at a 45 degree angle. The mirror 28 is custom manufactured from a segment of glass cut from a cylinder of glass at an angle. The face surface 42 of the glass is then polished and a reflective surface 44 is deposited on the face surface 42. In the manufacturing of mirrors, it is not economically practical to cut small elliptical shaped mirrors from a large flat mirror. As such, each of the mirrors 28 for the diopter cell assemblies are individually made by cutting a glass blank from a cylinder, polishing the face surface of the glass blank, and depositing the reflective surface onto the glass blank. Consequently, the costs associated with manufacturing the mirror 28 add significantly to the overall cost of the diopter cell assembly 24. Once the mirror 28 is manufactured, the mirror 28 is then manually placed within the housing of the diopter cell assembly 24. The mirror 28 is then manually aligned and affixed to the diopter cell assembly housing with adhesive.
The shown diopter cell assembly 24 is from a prior art AN/PVBS-7B night vision goggle device. In such a device each of the diopter cell assemblies include an L.E.D. The purpose of the L.E.D. is to superimpose a signal light over the image being viewed. For instance, a small light might may be superimposed over the viewed image to indicate to a viewer that the battery is low in the assembly or to indicate that an ancillary infrared light source has been turned on. In such a system, the L.E.D. is typically positioned within the diopter cell assembly 24 behind the mirror 28. As such, the L.E.D. creates a lighted figure on the mirror 28 that is superimposed over the image being viewed. Referring to FIGS. 2 and 3, it can be seen that a receptacle 46 for retaining an L.E.D. (not shown) is positioned on the back surface 48 of the mirror 28. The back surface 48 of the mirror 28 is not polished, as such a hole 50 is drilled into the mirror 28 from its back surface 48 toward its face surface 42, to allow light from the L.E.D. to pass through the material of the mirror. Furthermore, a segment 52 of the reflective surface 44 is removed from the face surface 42 of the mirror 28 in the region of the hole 50. As a result, light from the L.E.D. can pass through the hole 50 and pass through the removed segment 52 on the reflective surface 44 in order to create a viewable image on the surface of the mirror 28. In the prior art, the segment 52 of the reflective surface 44 removed is typically created by masking a small segment of the face surface 42 of the mirror as the reflective surface 44 is being deposited.
The receptacle 46 for holding the L.E.D. is held onto the back surface 48 of the mirror 28 by a double sided adhesive donut 54. The receptacle 46 is manually installed and is manually aligned over the drilled hole 50. The creation of an elliptical shaped mirror 28, the drilling of the hole 50 in the mirror 28, the removal of a segment 52 of the reflective surface 44, the placement of the mirror 28 in the diopter cell 28 and the attachment of the receptacle 46 to the mirror 28 combine to add significantly to cost by which such a prior art diopter cell can be manufactured.
It is therefore an object of the present invention to provide a diopter cell assembly for a binocular viewing system that is less complicated to manufacture, requires less labor to manufacture and is less expensive than prior art diopter cells for a given application.
It is a further object of the present invention to provide such a diopter cell assembly that can be interchanged with a prior art diopter cell assembly without necessitating and further changes in the overall binocular viewing system design.